On 11/26/2014 10:02 PM, Will Deacon wrote:
On Wed, Nov 26, 2014 at 04:49:47AM +0000, AKASHI Takahiro wrote:
If tracer modifies a syscall number to -1, this traced system call should
be skipped with a return value specified in x0.
This patch implements this semantics.
Please note:
* syscall entry tracing and syscall exit tracing (ftrace tracepoint and
audit) are always executed, if enabled, even when skipping a system call
(that is, -1).
In this way, we can avoid a potential bug where audit_syscall_entry()
might be called without audit_syscall_exit() at the previous system call
being called, that would cause OOPs in audit_syscall_entry().
Signed-off-by: AKASHI Takahiro <takahiro.aka...@linaro.org>
---
arch/arm64/kernel/entry.S | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 726b910..946ec52 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -161,6 +161,7 @@
*/
sc_nr .req x25 // number of system calls
scno .req x26 // syscall number
+scno_w .req w26 // syscall number (lower 32 bits)
stbl .req x27 // syscall table pointer
tsk .req x28 // current thread_info
@@ -668,8 +669,14 @@ ENDPROC(el0_svc)
* switches, and waiting for our parent to respond.
*/
__sys_trace:
- mov x0, sp
+ cmp scno_w, #-1 // set default errno for
I hate that we have to use scno_w, but the only alternative I can think of
is using w8 directly, which isn't any better and doesn't work for compat.
Ho-hum, I guess we'll stick with what you have.
The possible approaches might be:
* use 32-bit registers for scno & sc_nr and use "sxtw scno, w8," or
* use an extra reg like
__sys_trace:
mov x0, #0xffffffff
cmp scno, x0
b.ne 1f
+ b.ne 1f // user-issued syscall(-1)
+ mov x0, #-ENOSYS
+ str x0, [sp]
Can you use #S_X0 here for clarity, please?
Okey.
+1: mov x0, sp
bl syscall_trace_enter
+ cmp w0, #-1 // skip the syscall?
+ b.eq __sys_trace_return_skipped
adr lr, __sys_trace_return // return address
uxtw scno, w0 // syscall number (possibly new)
mov x1, sp // pointer to regs
@@ -684,6 +691,7 @@ __sys_trace:
__sys_trace_return:
str x0, [sp] // save returned x0
and update this guy too.
Sure.
-Takahiro AKASHI
Will
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